1. Field of the Invention
The present invention relates to a card edge connector which is a female connector provided on a printed wiring board or the like. Particularly, the present invention relates to a card edge connector provided with a crosstalk reduction structure.
2. Description of the Related Art
As disclosed in Japanese Patent Laid-Open No. 2007-149643, for example, a technique has heretofore been well known for electrically connecting printed wiring boards to each other by providing one of the boards with a plug connector serving as a male connector while providing the other board with a card edge connector serving as a female connector.
For the purpose of suppressing crosstalk, contacts in such a connector are desirable to be arranged in a coplanar structure in which ground contacts (G) are arranged across signal line contacts (S) for sending and returning signals, that is to say, in a G-S-S-G layout.
In recent years, however, crosstalk between adjacent signal line contacts has become a serious problem along with an increase in the signal transmission speed. In particular, for the high-speed transmission, an amount of crosstalk even in a higher frequency band needs to be reduced to a very small level.
In general, a connector for transmitting differential signals has a structure in which ground contacts are respectively disposed on both sides of two signal line contacts as in the G-S-S-G layout described above. When two pairs of signal line contacts are located adjacent to each other, the two pairs of signal line contacts are separated from each other by only one common ground contact as seen in a G-S-S-G-S-S-G layout.
Ground wires to be located on a printed wiring board are connected to one another by use of a ground common plane or the like inside the printed wiring board, and are configured to have the same electric potential. On the hand, in a connector, multiple contacts are connected to the printed wiring board through only two contacts located on both end sides. In this case, the ground contacts are located at a distance from the ground common plane provided inside the print wiring board. For this reason, the ground contacts have different electric potentials, which are also different from an electric potential of the ground wires on the printed wiring board. Accordingly, the ground contacts degrade their shielding effects against high-frequency signals having a frequency component of several GHz. As a consequence, there is a risk of causing a problem of an increase in the crosstalk with an adjacent signal line contact or with a signal line contact next to the adjacent one.
With the problem taken into consideration, an object of the present invention is to provide a card edge connector as a high-speed differential signal connector configured to equalize electric potentials of ground contacts adjacent to signal line contacts, and thereby to reduce crosstalk between adjacent signal line contacts.